Titanium dioxide (titania) is well known and has a variety of applications, including cosmetics, personal care products, plastics, surface coatings, self-cleaning surfaces, drug delivery and medical devices, as a catalytic carrier material and in photovoltaic applications.
There are two main processes for making raw titanium dioxide: the sulfate process and the chloride process.
The sulfate process is based on the digestion of ilmenite or titania slag in concentrated sulfuric acid. After iron removal as iron sulfate, the solution is heated and diluted with water. The titanium hydrolyzes, forming a titanium oxysulfate precipitate, which is further treated to produce TiO2 pigment.
The chloride process relies on carbochlorination of titanium containing ore or intermediate products to form TiCl4, followed by the gas phase oxidation of TiCl4.
Titanium dioxide can be flocculated and/or precipitated out of a slurry containing titanium dioxide by pH adjustment of the slurry.
The finishing process for titanium dioxide, as obtained by any known method, may include one or more of: drying, milling, filtering, washing, and packaging.
Many applications require the titania to have a large specific surface area (e.g. greater than 200 m2/g), in order to increase efficacy. In particular this is due to the fact that such larger surface areas result in increased gas to solid contact ratios or increased liquid to solid contact ratios. Such large specific surface areas can be achieved by the use of nano particles of titania (i.e. particles with a diameter of less than 100 nm) and this is the current normal approach.
However, the use of nano materials has attracted publicity and concerns from some areas. In general, there has been much debate generated with regard to the environmental health and safety implications of nano materials.
There can also be applications where control of the surface area/porosity to be within certain ranges can be desired; the largest possible specific surface area is not always what is required.
There is also a desire for titania material that has a particle shape suited to the desired end use of the material. Dependent on the intended use, different shapes of particles may be more appropriate.
Thus it has been identified by the inventors that there is a clear need for methods that permit control of morphology (i.e. form and structure) when manufacturing titania particles. The morphology may in particular relate to the pore size in the titania particles (which in turn impacts on the specific surface area of the particles) and/or the shape of the titania particles (e.g. in terms of whether the particles are spherical in shape or present an alternative shape such as a toroid (i.e. a doughnut-type shape), and whether the particles are “fluffy” or have a smooth surface).
In this regard, it is particularly desired to be able to control porosity (and thus specific surface area) when manufacturing titania particles and/or to control particle shape when manufacturing titania particles, in order that particles having a suitable porosity and/or shape for the desired application can be prepared.